PROJECT SUMMARY Proper visual function relies on all the cell types in the retina being generated in the correct proportion and at the correct developmental time. However, our understanding of how neural progenitors determine which cell fates to produce during retinogenesis in the embryo has remained ambiguous. We know that retinal cells are generated from a common pool of retinal progenitors that shift their competence over time to give rise to seven retinal cell types in a stereotypic sequence. But, we do not know the mechanisms that control competence transitions, and our understanding of retinal cell fate determination is incomplete. Recent studies have shown that microRNAs (miRNAs), short, single stranded nucleic acid molecules that negatively regulate gene expression, are required for retinal progenitor cells to transition from producing early- to late-born retinal cell types; but, we do not know their mechanism of action. My preliminary data suggests that miRNAs regulate cell cycle kinetics in retinal progenitors, and has led to my hypothesis that miRNAs mediate progenitor competence by controlling cell cycle length. In this proposal, I will test my hypothesis via the following Aims: Aim 1: To determine how late-progenitor miRNAs regulate cell cycle dynamics in retinal progenitors. Aim 2: To determine how retinal progenitor cell cycle length impacts cell fate. Aim 3: Determine if miRNA-directed changes in cell cycle dynamics mediate the development of the chicken high acuity area. I will use a combination of in vivo and in vitro techniques; including, flow cytometry, live imaging of retina explants, RNA-sequencing and chick embryo electroporation to answer my research questions. This will greatly expand my technical skillset, which will help me become a more competitive candidate for a faculty position. In addition to expanding my technical skills, in my research training plan I address the soft skills required for my success as an academic researcher by assembling a group of experienced mentors who will provide mentorship in the following categories: Career development, teaching, grant writing and science outreach. UC Davis provides a very collaborative environment and access to top-notch core facilities; thus, it is an ideal environment for me to perform my experiments and enhance my career development skills. Successful completion of the project outlined here will provide crucial insight into the mechanisms that control neural progenitor cell fate decisions. This information is crucial to establish efficient protocols for generating donor cells from stem cells, which can subsequently be used for cell replacement therapies to treat degenerative diseases like age-related macular degeneration.